Composite materials, and particularly core composite constructions, have a broad range of application in high-technology fields, such as aircraft construction or automobile construction, because of their good ratio of rigidity and strength to density. Core composites typically comprise two cover layers made of materials to be selected specifically for the application, and a core structure located between the cover layers.
Such core composites may, for example, comprise a hard foam core, into which dry fibers are sewn by using sewing methods. The dry fibers are embedded in a matrix in a downstream infusion process.
In a further exemplary production process, instead of the sewing method, rod-shaped stiffening semifinished products, such as pins, may be introduced into the foam. These rod-shaped stiffening semifinished products may be produced, for example, in a pultrusion process. In these production variants for semifinished products, the fibers are drawn through a nozzle, which predefines the later semifinished product cross-section. The initially dry fibers are impregnated either by the passage through a resin bath, or by a special infusion process using resin. The resin matrix cross-links by heating the nozzle. To guarantee dimensional stability after exit from the pultrusion tool, the matrix must be either completely cross-linked, or it must have achieved at least a sufficient partial degree of cross-linking. These stiffening semifinished products are subsequently introduced into the foam. Mechanical properties may be defined and varied via the material, the reinforcement density, and the angle of the stiffening semifinished products.
The foam is thus used on one hand as a carrier, which holds the stiffening semifinished products in position, on the other hand the foam is used for stabilizing the stiffening semifinished products to prevent or at least delay their buckling under a load, for example.
U.S. Pat. No. 6,190,602 B1 describes a production method of a sandwich construction comprising a core having stiffening semifinished products. Before the curing of a hard foam and/or a laminate, the stiffening semifinished products are introduced using a tool. The stiffening semifinished products connect the two cover layers and support the bonding of the cover layer to the hard foam. The tool may introduce the stiffening semifinished products into the layers using ultrasound.
U.S. Pat. No. 6,291,049 B1 describes a sandwich structure and a production method of this sandwich structure. The sandwich structure has a top and a bottom cover layer, between which a foam core is situated. Reinforcement semifinished products, which reinforce the sandwich structure, are attached by the cover layers and the foam core.